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Recent Research in the African Great Lakes: Fisheries, Biodiversity and Cichlid Evolution

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Recent Research in the African Great Lakes: Fisheries, Biodiversity and Cichlid Evolution Recent research in the African Great Lakes: fisheries, biodiversity and cichlid evolution Item Type article Authors Lowe-McConnell, Rosemary Download date 30/09/2021 23:17:08 Link to Item http://hdl.handle.net/1834/22270 4 RO LOWE-MCCONNELL RECENT RESEARCH IN THE AFRICAN GREAT LAKES: FISHERIES, BIODIVERSITY AND CICHLID EVOLUTION ROSEMARY LOWE-McCONNELL Dr R. H. Lowe-McConnell, Streatwick, Streat Near Hassocks, Sussex BN6 8RT, UK Abstract The East African Great Lakes are now well known for (1) their fisheries, of vital importance for their rapidly rising riparian human populations, and (2) as biodiversity hotspots with spectacular endemic faunas, of which the flocks of cichlid fishes unique to each of the three largest lakes, Tanganyika, Malawi and Victoria, offer unique opportunities to investigate how new species evolve and coexist. Since the early 1990s research involving over a hundred scientists, financed by many international bodies, has produced numerous reports and publications in widely scattered journals. This article summarizes their main discoveries and examines the status of, and prospects for, the fisheries, as well as current ideas on how their rich endemic fish faunas have evolved. It first considers fisheries projects in each of the three lakes: the deep rift valley lakes Tanganyika and Malawi and the huge Victoria, all of which share their waters between several East African countries. Secondly it considers the biodiversity surveys of each lake, based on underwater (SCUBA) observations of fish ecology and behaviour which have revealed threats to their fish faunas, and considers what conservation measures are needed. Thirdly, using the lakes as laboratories, what have the international investigations (including DNA techniques and follow-up aquarium experiments) now revealed about the origins and relationships of their cichlid species flocks and mechanisms of evolution? Introduction The African Great Lakes, especially Tanganyika, Nyasa/Malawi and Victoria, are now well known from a voluminous literature as hotspots of biodiversity, the flocks of endemic cichlid species, with their spectacular adaptive radiations to use all kinds of foods, providing unique material for evolutionary studies. The lakes also support fisheries vital for the rapidly growing riparian human populations. As a young fisheries research officer I spent happy years (1945-54) studying these beautiful lakes for the East African Fisheries Research Organisation. Fifty years later I am naturally curious to know: (a) how their fisheries have developed, (b) whether their Freshwater Forum 20 (2003), 64 pp. © Freshwater Biological Association 2003 FISHERIES OF THE AFRICAN GREAT LAKES 5 faunas are still as diverse, and (c) what advances have been made in understanding the origin and evolution of their most remarkable endemic cichlid fish faunas. Others might also find it useful to have this overview as many recent findings are published only in journals and reports with restricted distributions. This review concentrates on the state of the fisheries, conservation of biodiversity, and cichlid evolution in the three lakes on which I worked for many years. These are the very old deep rift-valley lakes Tanganyika and Malawi and the huge saucer (69 000 km2, < 90 m deep) of Lake Victoria, its equatorial waters shared by Tanzania, Uganda and Kenya (Fig. 1). These lakes have been the main focus of recent research as they have the most important fisheries, on which the rising human populations (now estimated at some 287 million around these lakes) rely for their protein. They also have the most diverse faunas (now threatened by anthropogenic impacts), and in them the most spectacular flocks of endemic cichlid species have evolved, which provide unique material for scientific studies of worldwide interest on the evolution of new species and their co­ existence (Fig. 2). For reasons of space, little can be included about studies on the smaller African lakes, though these too support fisheries and are helping to reveal cichlid relationships throughout the region. For example, in many satellite lakes swamps have provided refuges for certain species (e.g. papers by Chapman et al. 1996, 2003), and in the Lake Rukwa drainage (Seegers 1996) and in Cameroon crater lakes cichlid species appear to have evolved sympatrically (some useful references are given in Lowe-McConnell 1991, 1995, 2000; Leveque 1997, 2001; Turner et al. 2001,Crismanetal. 2003). In 1987 I was 'volunteered' to be Convenor of the African Great Lakes Group of the International Limnological Society (SIL), formed at SIL's New Zealand Congress in response to George Coulter's concern that drilling for oil had started on the shores of Lake Tanganyika; such drilling could endanger priceless fauna, fisheries and water supplies for the four riparian countries, Burundi, Tanzania, Zambia and Zaire (now Democratic Republic Congo). The Group's first task was to organize an 'International Symposium on Resource Use and Conservation of the African Great Lakes', on Lake Tanganyika at the University of Burundi, Bujumbura in 1989. With the kind co-operation of Frits Roest of the Fisheries Unit of IAC in Wageningen, Netherlands, this symposium was attended by over 100 people from 21 countries (including many African participants). It provided the first opportunity for people of many disciplines to discuss fish stocks and fisheries, water quality and vulnerability to pollution, the International Agricultural Centre Freshwater Forum 20 (2003) 6 RO LOWE-MCCONNELL 30° E 35° E 40° E 45° E FIG. 1. The Great Lakes of eastern Africa - Victoria, Tanganyika and Malawi (also called Nyasa in Tanzania and Niassa in Mozambique) - with associated river systems, indicating barriers (waterfalls and rapids) important in the isolation of the various basins. Reproduced with kind permission of Kluwer Academic Publishers, from Lowe- McConnell (1996): Environmental Biology of Fishes, vol. 45, p.220. Fig. 1 (with minor modification). Freshwater Forum 20 (2003) FISHERIES OF THE AFRICAN GREAT LAKES 7 Non-cichlids Cichlids FIG. 2. Representatives of Lake Tanganyika's 23 families of non-cichlids and 12 tribes of cichlids (scale bars = 20 mm). Non-cichlids: a) zooplanktivorous clupeid; b) piscivorous hates; c) carnivorous bagrid catfish; d) omnivorous clariad catfish; Cichlids: e) piscivorous Boulengerochromis; f) carnivorous crevice-feeder Lamprologus; g) bottom-sand sifter Trematocara; h) algal-grazing Petrochromis. Modified, with kind permission of Kluwer Academic Publishers, from Lowe- McConnell (1996): Environmental Biology of Fishes, vol. 45, p.221, Fig. 2. Freshwater Forum 20 (2003) 8 RO LOWE-MCCONNELL scientific value of the lakes and conservation measures (IAC 1990a, b; Lowe-McConnell et al. 1992). A subsequent conference in Bujumbura concentrated on 'Conservation and Biodiversity of Lake Tanganyika' (Cohen 1991). The widely circulated recommendations from these two meetings were then used to apply for international funds for fisheries and biodiversity projects. Sources of information The 1990s saw a veritable explosion of research. It had already become clear that all three lakes were facing serious anthropogenic threats caused by the rapid rise in human populations, leading to overfishing and pressures on biodiversity from sedimentation and pollution resulting from changes in land use in the lake basins. Large projects and workshops (listed in Appendix 1) included the FA02/FINNIDA3 Lake Tanganyika Research Project (LTR), financed by Finland and executed by FAO, which examined the sustainability of Lake Tanganyika's commercial pelagic fisheries; the UK/SADC survey which explored the offshore waters of Lake Malawi for new pelagic fish stocks; and a Lake Victoria Fisheries Research Project (LVFRP) financed by the EU5 which examined the prospects for Victoria's fisheries, much changed since the establishment of the predatory Nile perch (Lates niloticus), introduced to the lake in the mid-1950s. International interest in conservation of biodiversity was stimulated by the Biodiversity Convention signed at the Rio Earth Summit in 1992. This enabled United Nations agencies to set up projects using GEF6 funds for biodiversity studies on lakes Tanganyika and Malawi and for a Lake Victoria Environmental Management Project (LVEMP). In addition to the very numerous reports and widely scattered scientific papers from these projects, ongoing research on all three lakes also contributed abundant new information. In particular, from the clear waters of Lake Tanganyika, Japanese and African scientists, organized since 1977 by H. Kawanabe of Kyoto University, used SCUBA to observe the ecology and behaviour of the numerous endemic cichlid species cohabiting in the lake's highly diverse rocky shore communities (Kawanabe et al. 1997). In Lake Victoria, Leiden University's Haplochromis Ecology Survey Team (HEST) from The Netherlands, together with the Tanganyika Fisheries Research Institute (TAFIRI), continued research initiated in 1977 in Tanzanian waters at the Food and Agriculture Organization of the United Nations Finnish International Development Agency Southern African Development Community European Union Global Environmental Facility Freshwater Forum 20 (2003) FISHERIES OF THE AFRICAN GREAT LAKES 9 south end of the lake (producing a number of PhD theses which include their published papers, e.g. Wanink 1998; Seehausen 1999). Looking for cichlid refuges from the Nile perch, HEST discovered a whole new group of 100+ species of rock-dwelling cichlids,
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